A push-to-talk (PTT) service provides direct one-to-one and/or one-to-many audio communication. PTT may include a mechanism that provides instantaneous communication between parties, and that utilizes a button to switch user equipment (UE) from a voice transmission mode to a voice reception mode. The operation of UEs in this manner may be similar to how walkie talkies operate. A PTT service may switch a UE from a full duplex mode, where both parties may hear each other simultaneously, to a half duplex mode, where a single party may speak at one time. Multiple parties or a group conversation may also be provided by a PTT service. Availabilities of parties may be checked before a call with the help of a presence function.